In general, an automatic player piano has a plurality of keys coupled to respective key action mechanisms, and each of the keys is driven by a solenoid-operated key actuator unit for producing a sound. A typical example of the automatic player piano is disclosed in Japanese Utility Model Application laid-open Kokai) No. 113584/1980 and the general arrangement thereof is illustrated in FIG. 1 of the drawings. In FIG. 1, reference numeral 1 designates a keyboard unit consisting of a plurality of white and black keys 2 and 3 each accompanied by a key action mechanism 4, and each of the keys is rockably supported by a balance rail 5 provided on a key bed 6, so that the key action mechanism 4 is driven for causing a hammer ( not shown ) to hit a string 7 when the key is pressed by a player. The automatic player piano illustrated in FIG. 1 further comprises a plurality of solenoid-operated key actuator units 8 and 9 each provided in association with each of the keys which is connected at a rear end portion thereof to the solenoid-operated key actuator unit. Each of the solenoid-operated key actuator units 8 and 9 is energized by a controller 10, so that the key mechanism 4 is driven for causing the hammer to hit the string 7 upon activation of the solenoid-operated key actuator unit.
Turning to FIG. 2 of the drawings, solenoid-operated key actuator units 11 and 12 are illustrated in association with a key board 13 consisting of a plurality of keys including a key 14, and this arrangement is disclosed in Publication of Japanese Utility Model Application ( Kokoku ) No. 15838/1987. The solenoid-operated key actuator units 11 and 12 are supported by a retainer 15, and the retainer 15 is attached at upper and lower end portions thereof to a bracket member 16 which in turn is fixed to the lower surface of a key bed 17. Each of the solenoid-operated key actuator units 11 and 12 largely comprises, as shown in FIG. 3, a cylindrical guide member 21 formed of brass, a coil bobbin 22 snugly received on the outer surface of the cylindrical guide member 21, a coil wire 23 wound on the outer surface of the coil bobbin 22, a movable member 24 slidably received in the cylindrical guide member 21, a covering member 25 attached to the coil bobbin 22 for covering the coil wire 23 and a plunger 26 connected to the movable member 24 to drive the key. The solenoid-operated key actuator 11 or 12 thus arranged deeply retracts the movable member 24 in non-activating state as will be seen from FIG. 3, however the movable member 25 is moved in the cylindrical guide member 21 to allow the plunger 26 to upwardly push the rear end portion of the key when the coil wire 23 is supplied with a current. In this arrangement, magnetic saturations take place around the top and bottom end portions of the cylindrical guide member 21, so that the movable member 24 is designed to move into a magnetic equilibrium position when the actuator is energized.
However, a problem is encountered in the prior-art automatic player piano illustrated in FIG. 2 in that various solenoid-operated key actuators different in size are needed for a line of products different in size and model from one another. This is because of the fact that the automatic player piano of one model has a key action mechanism different in size and/or arrangement from that of another model. The key action mechanisms are thus different from one another depending upon the piano model, so that the solenoid-operated key actuators should be designed to correspond to the differences among the key action mechanisms of the different piano models.
Moreover, if the solenoid-operated key actuator illustrated in FIG. 3 is used in the automatic player piano, another problem is encountered in occupation space of the solenoid-operated key actuator. Namely, the solenoid-operated key actuator illustrated in FIG. 3 has a relatively long length in the moving direction of the movable member 24, because the key actuator needs to provide a relatively long driving stroke as it drives a key at a point relatively distant from the balance rail 5.